Manual dexterity of son with learner crew (7)
I believe the answer is:
sleight
'manual dexterity' is the definition.
('sleight' can be a synonym of 'manual dexterity')
'son with learner crew' is the wordplay.
'son' becomes 's'.
'with' says to put letters next to each other.
'learner' becomes 'l'.
'crew' becomes 'eight' (I've seen this before).
's'+'l'+'eight'='SLEIGHT'
'of' acts as a link.
(Other definitions for sleight that I've seen before include "Artful trick" , "Handy skill" , "Trickery" , "distraction?" , "Cunning action" .)